The CF part of the barrel is about 0.83” +/- 0.01”.
The black aluminum part on the barrel is the correct diameter, and will support about 1” stroke of the back of the pump handle, but the rest of the CF barrel is undersized so the pump handle will be sloppy over most of the range.

A sleeve could be made to go over part of the CF to let the handle slide without front slop… but you would have to do this yourself-- we currently do not have a ready solution for it.
That is why we list them for "Under-cocking" only.

I use a stock pump handle on my DW barrel and havent noticed a thing yet. Played "Red Strike" at blast camp with it the whole weekend and at least a dozen other days and see no "wear" marks or anything.

My DW barrel slides right through my pump handle and screws into the marker without issue. I mean its a tiny bit snug to slip it through but doesnt require much push to get it through it.